Spark plug



. Aug. 15, 1944. A. c. HASTINGS, JR., ET AL SPARK PLUG iled M24714 1941 3& 511} \k 30 44% in" I 25 v 23 z I I we 2 ?o 54 JaJ ENTORS Patented Aug. 15,

UNITED STATES PATENT OFFICE SPARK PLUG Arthur 0. Eastman, Orlando B. Hastings, and Wallis R. Horsfleld, South Yarmouth, Mass.

Application May 14,1941, Serial No. 393,366

Claims.

is a cross sectional view of a spark plug embodying the present invention; and Fig. 2' is across sectional view of a modified form of spark plug embodying the invention.

In general, the present invention aims to provide a novel construction of a spark plug of the type illustrated and described in the United States Patent to Hastings, No. 2,069,951, issued February 9, 1937, and which is particularly adapted for use as a shielded spark plug for aeronautical use. One feature of the present invention resides in the provision of a moulded insulator formed within a socket in the upper P rtion of the metallic shell or outer electrode and In th drawing illustrating the invention, Fig. 1

inner electrode l and a tubular insulating member ll preferably of a ceramic composition. As I shown inFig. 1, the tubular insulator H is reduced in outside diameter at its lower end and is arranged with the inner electrode to substantially fill the bore within the outer electrode and to terminate in substantially the plane v of the outer electrode to the end that during the operation of the plug, sparks are caused to traverse across the endof the insulating member. The

lower end ofthe inner electrode or firingpin I2 is comprise adetachable member 20 having a I about the upper portion of the inner electrode and a portion of an inner tubular ceramic insulator whereby to form a gas tight and electrically tight bond. The upper portion of the outer metallic shell may be detachable and such upper portion together with the inner electrode and the ceramic tubing may be secured together by the moulded insulator to form a replaceableunit. Themoulded insulator may and preferably -will comprise an 1 insulating composition such as a phenolic-formaldheyde resinous composition or other suitable insulating material characterized by a transformation from an initial fusible and reactive state to a final infuslble one upon heating.

Another feature of the invention resides in a shielded spark plug of novel and improved construction having novel connecting means arranged to receive an adapter formed on the end of an insulated cable connector by which. the distance through which the current must pass to form a short circuit between the top of the plug and the top of the inner electrode is materially lengthened without increasing the overall length of the plug. l

Referring now to the drawing, It represents an outer metallic electrode having a longitudinally extended bore within which are positioned the preferably reduced in diameter to receive a platinum sleeve it which may be silver soldered to the inner electrode, and the lower end of the outer electrode may be bored out as shown to receive a platinum sleeve 3- similarly secured thereto in order to provide efllcient sparking contacts;

l The outer shell or metallic electrode [6 is exv tended for the full length of the plug to form aprotective metallic shell for shielding the plug, and as herein shown, the upper end thereof. may

threaded connection with the main body portion M of the plug.

As illustrated in Fig. 1,-the upper portion of the metallic shell 10 and the detachable portion 20 thereof are provided with an enlarged bore or socket through which the ceramic insulation and the inner electrode extend, the inner electrode being extended for the full length of the plug and substantially flush with the top of the outer shell. An asbestos gasket 22 is 'provide'd'at the lower end of the enlarged bore between the outer electrode and the ceramic tube H in order to form a protection for the moulded insulation against hot gases of combustion passing upwardly between the ceramic tube and the metallic body of the plug.

With the parts in their assembled relation thus far described, the phenolic resin, Micalex or' other mouldable plastic, in its fusible state is introduced into the bore or socket oi the outer shell to form a body of insulation 24 within the socket and about a portion of the ceramic tube l4 be moulded in the plastic insulator 24 to forma firm bond therewith.

As shown in F18. 1, the upper portion of the 'inner electrode i2 is preferably provided with grooved portions 28 in order to eflect a firm bond between the plastic insulator 24 and the upper portion of the inner electrode, and in practice, such upper portion may and preferably will be provided with a thin coating of Vinylite resin or other equivalent thermoplastic material, as indicated by the stipple work 25, such material preferably having. substantially the same fusing temperature as the plastic insulator in order to provide a more eillcient bond and to form an efficient gas tight seal between the plastic insulator and the center electrode. An annular metallic member 30 is secured about the top of the center electrode It, as shown, in order to increase the 'eil'ective contact surface with the lead-in cable connector, as will be described.

As herein shown, the cable connector comprises an insulating elbow, one arm 32 of the elbow being detachably secured to the top of the sparkplug and enclosing a conductor 34, and the other arm 36 enclosing a cable lead 38. The elbow is provided with a metallic outer shell it havmg a flanged portion 2 at its connecting which is engaged by a nut 4! arranged to be J r 53, as hidicated, is formed from a ,ulclerl pie insulating material, and as hereshown, is provided with an annular skirt 52 which is arranged to be received within an ennular groove 5 formed in the top of the insulator 2 3 of the spark plug. The lower end of the conductor 3% may provided with the usual spring connection in engagement with the top of the.

electrode it.

From the description thus far, it will be observed that the above described construction of shielded spark plug is such asto reduce to a minimum the dissipation of the current through leakage paths. The manner of engagement of the adapter 5 with the top of the spark plug is such as to provide a greatly increased leakage path from the top of the inner electrode l2 and the top of the outer shell of the spark plug without increasing the length of the plug and may permit a reduction in the length of the plug to adapt it for use in limited spaces. As herein shown, the path of leakage between the top of the inner electrode l2 and the top of the outer shell is lengthened by the annular skirt 5! to require the current to pass downwardly in the groove 54 and then upwardly on the outer surface of the skirt before it can reach the top of the spark plug. Asis known, the connecting memher in a conventional commercial form of shielded spark plug extends down into the interior of the plug to provide a leakage path of approximately three quarters of an inch. with the present construction, this leakage path may be increased to approximately one and oneeighth inches without increasing the overall length of the spark plug. This increased leakage aeaaoss path is particularly desirable in an aircraft spark plug since the resistance to such leakage is materially reduced at high altitudes. For the purpose of enhancing heat conduction, the outer walls of the plug may be ribbed, as shown, although for most purposes this feature is not necessary.

Referring now to Fig. 2, a modified form of a shielded spark plug may include an outer elecarranged to rest against a shouldered portion II within the lower shell, as shown. A suitable gas ket 12 may be provided between the shoulder 1. and the main insulator. The upper shell 62 .13 extended within the lower shell to form a shoulder 14 arranged to engage the upper part of the enlarged portion 68 of the main insulating tube 86. A second gasket 16 may be provided between these surfaces whereby to prevent the hot gases of combustion from leaking between the insulator G8 and the lower shell 60.

The main insulating tube 65 extends upwardly into the upper shell Bl for a substantial distance, as shown, and a second insulating tube 18 extending from the top of the plug and downwardly beyond the top of the main insulator 66 is arranged to be inserted between the upper shell II and the main insulator 86 carrying the inner electrode 68. Thus, an insulated socket I0 is formed in the top of the plug which is arranged to receive the conventional shielded connector indicated generally by the numeral 82.

The lower end of the porcelain insulator 86 may be tapered as shown and filled into a correspondingly tapered socket in the outer electrode, and the ends of the outer and inner electrodes and the insulator are preferably arranged to terminate in substantially the same plane so that during operation the spark is caused to travel across the end of the insulator.

While the preferred embodiments of the invention have been herein illustrated and described, it will be understood that the invention may be embodied in other forms within the scope oi the following claims.

Having thus described the invention, what is claimed is:

1. A shielded spark plug comprising an outer,

electrode including an elongated hollow metallic member, an inner electrode coextensive with the length of said outer electrode, an elongated tubular insulating member positioned between said electrodes for a major portion thereof, and a moulded insulating member within the upper portion of said hollow member and surrounding the upper portion of said inner electrode and said tubular insulating member whereby to form a substantially gas tight bond between said upper portions of the plug, said outer electrode including a detachable upper portion whereby to form a replaceable unit with said moulded insulator, tubular insulator and inner electrode.

2. A shielded spark plug comprising an outer electrode including an elongated hollow metallic member, an inner electrode coextensive with thelength of said outer electrode, an elongated tubular insulating member positioned between said electrodes for a major portion thereof and a moulded insulating member within the upper portion 0! said hollow member and surrounding the upper portion of said inner electrode and said tubular insulating member whereby to form a substantially gas tight bond between said upper por tions of the plug, the upper portion 0! said inner electrode being provided with a thin coating of a thermoplastic binder having a softening temperature approximately the same as said moulded insulating member whereby to provide a gas tight seal between the latter and said inner electrode.

3. A shielded spark plug comprisingv an outer electrode including an elongated hollow metallic member, an inner electrode coextensive with the length of said outer electrode, an elongated tubular insulating member positioned between said electrodes for a major portion thereof, and a moulded insulating member within the upper portion of said hollow member and surrounding the upper portion of said inner electrode and said v upper portions of the plug.

4. A shielded spark plug comprising an outer electrode including an elongated hollow metallic member, an inner electrode coextensive with the length of said outer electrode, an elongated tubular insulating member positioned between said electrodes for a major portion thereof, and a moulded insulating member within the upper portion or said hollow member and surrounding the upp r portion of said inner electrode and said tubular insulating member whereby to form a substantially gas tight bond between said upper portions of the plug, said outer electrode including a detachable upper portion whereby to form a replaceable unit with said moulded insulator, tubular insulator and inner electrode, and a metallic gasket between said detachable portion and the body portion of said outer electrode and moulded to said moulded insulating member.

5. A shielded spark plug comprising an outer electrode including an elongated hollow metallic member, an inner electrode coextensive with the length of said outer electrode, an elongated tubular insulating member positioned between said electrodes for a major portion thereof, and a moulded insulating member within the upper portion of said hollow member and surrounding the upper portion of said inner electrode and said tubular insulating member whereby tov form a substantially gas tight bond between said upper portions" of the plug, the upper portion of said moulded insulator being provided with an annular groove arranged to receive a cable lead contact adapter whereby to materially increase the leakage path of the current between the upper portion of said inner electrode and the top of said 

